1. Field of Invention
The invention relates to an electricity element, a separator thereof and a manufacturing method of the separator.
2. Related Art
3C products, such as electronic, information and communication devices, are gradually developed toward the wireless and mobile directions. Various high-performance elements used in various products have to be developed toward miniaturization. In addition, the development of the flexible electronic product has also been gradually emphasized in the recent years. Thus, the need of the battery having small size, light weight and high energy density is very urgent.
Regarding to the usage property of the battery system, a conventional primary battery system, which cannot be repeatedly used, cannot satisfy the requirement of the modern electronic product in order to lengthen the using time and increasing the energy density of the battery. The mainstreams in the battery systems applied to the electronic products are now the secondary battery systems, which can be charged and discharged repeatedly. The secondary battery systems include, for example, a lithium battery system, a fuel cell system, a solar cell system, and the likes. However, under the development of the modern technology, the fuel cell system still encounters the limitation of the minimum size, and the solar cell system cannot obtain the ideal energy conversion efficiency due to the limitation of the material. Therefore, the lithium battery system among the secondary battery systems is well developed and can achieve the requirements of the small size and high energy density.
The battery core structure of the lithium battery is gradually developed from the stacked structure to the wired structure. The main structure of the battery core in either the stacked structure or the wired structure includes an anode plate, a cathode plate and a separator interposed therebetween. Referring to FIG. 1, a conventional battery 1 includes a separator 11, a first current collecting layer 12, a second current collecting layer 13, a first active material layer 14, a second active material layer 15 and a package unit 16. The separator 11 has a separator body 110, a first film 111 and a second film 112. Alternatively, the separator 11 can be composed of the separator body 110 only. The separator 11 mainly prevents a first electrode substrate, which includes the first current collecting layer 12 and the first active material layer 14, from directly contacting with a second electrode substrate, which includes the second current collecting layer 13 and the second active material layer 15. The configuration of the separator 11 is to prevent the short-circuited condition in the battery 1 and to provide the path for ion migration in the battery 1. Therefore, the material of the separator body 110 of the separator 11 must have the non-electrical conductive and porous properties. The separator body 110 is usually made of a polymeric material, such as polyethylene or polypropylene, and the holes of the separator body 110 are usually formed by non-solvent system or mechanical uniaxial tension technology.
The structure of the local polymer can be transformed within a predetermined temperature range according to softening temperatures (about 100 to 150° C.) of different polymers or the same polymer with different molecular weights. Thus, when the battery system has the internal short-circuited condition, the external short-circuited condition or any factor, which causes the rise of its internal temperature, the path for the ion migration in the battery 1 can be closed due to the structure transformation of the separator body 110 and films 111, 112 of the separator 11. Accordingly, the battery 1 can be prevented from continuing the electrochemical reaction at the high temperature so as to decrease the possibility of the explosion of the battery 1.
However, if the temperature of the battery 1 continuously rises up to 150 to 180° C., the separator 11 may melt and break down to cause the overall short-circuited conditions and thus the seriously firing or exploding condition
Therefore, it is an important subject to provide a separator capable of withstanding high temperature.